Heat developable copy sheet and compositions useful therefor



United States atent 1" 3,076,707 HEAT DEVELOPABLE COPY SHEET ANDCOMPOSITIONS USEFUL THEREFOR WilliamR. Lawton and Eugene -F. Lopez,Nashua, NH, .assignors to NashuaCorporation, Nashua, N .H., acorporation ofDelawai-e "NDrawing. Filed Apr. -22, 1959, Ser. No.808,012 8 Claims. (C13 96--75) This invention relates to the duplicatingarts 'an'd pro- :vides a heat-developable cor'n'posit-iom-an'd moreparticularlya photosensitive compositionthatmay be developed -to.producea colored image simply by the application of heat. Thecomposition is accordingly ideally suited asthe sensitive component ofthermographic and photographic "copy-sheets of the direct exposure type,and sheets embodying theinventionareinexpensive, stable and ofutanosttconvenience in use. A copy may be formed by exposing thetsheetto ultraviolet rays through a masterand .then heating it to .produce avisible duplicate of the master. Copysheets embodying this invention maybe stored without deterioration for considerable periods of time, uptoseveral months at ordinary temperatures, and under conditions ofrelatively high humidity, and when used for copying :purposes theycombine the versatility, cleanliness andLpermanence'of copy of thediazotype sheet :With the speed and convenience of the thermofacsimiletype sheet.

Of the numerous systems available for making copies of graphic works,the most useful for general office use, Where only one or a fewcopiesare desired, are those that provide copy directly by contact exposure ofthe copy sheet to the master. Three types of system in common use arethe silver emulsion type, the diazo type and the thermofacsimile type.Of these only the last two provide a direct copy (positive); the silveremulsion type produces a negative by direct exposure which is then bychemical means transferred in reverse to a positive sheet. Thethermofacsimile type is the most convenient to use, for it simplyrequires a single exposure of the copy sheet to the master underinfrared radiation, and the copy is produced directly in a singleexposure. The copy, however, suffers from the disadvantage of not beingsharp and distinct, and subsequent heating will cause a darkening in themanner of an original exposure and obliterate the copy. The sheetscurrently available for thermofacsimile copies are moreover formed ofmaterials transparent to thermal radiation, and lack the texture,finish, stiffness and body of paper.

Diazotype copy sheets, on the other hand, produce a copy which isgenerally superior to thermo'facsimile in clearness, distinctness,sharpness, contrast and permanence, and the sheets may be formed on anykind of paper or other backing material, which permits any desiredtexture or other character. Diazotype sheets presently availablecommercially, however, require a treatment subsequent to the exposure todevelop the copy. Generally the sheet is either brought into contactwith ammonia vapors, as in the Ozalid type, or is treated with a basicsolution reactive with the photosensitive material in the sheet, as inthe Bruning type sheet. In either case, additional equipment andprocessing is necessary following the exposure of the sheet.

Diazotype copy sheets are conventionally dependent on the fact thatcertain diazonium compounds are light sensitive and decompose whenexposed to actinic rays. The same compositions are dyestutf componentsand react under basic conditions with a class of compounds, certainphenols, known as azo couplers, to form dyes. Upon exposure of thediazotype copy sheet to actinic rays, the diazo compound in the exposedarea is destroyed, remain- ,Fice

The formulation of the photosensitive coatingon'couve'ntional*diazoshe'ets may'include'only thediazoniurn compound, in which casedevelopment is'brou'g'ht about -by treatin'gthe sheetwith adevelopersolution containing the az'o'coupler compound and a base.Alternatively, the coating may include both components of 'the diazosystem, the diazo'nium compound and the azo coupler, "t'

' geth'e'r "with-stabilizers (such as urea and thioii'rfeaf) and acidmaterial which prevents prema ur reaction between the diazonium compoundandthe'azocouplercompound.

Such a paper' may b'e developed-'simply by applyinga base,

'itnost conveniently by exposure to ammonia vapors, 'and is-"generallyreferred to'as an ammonia'developing diazotype paper. a I V The presentinventionis directed primarily to improving the versatility" andconvenience of diazotypecopylcompositions by incorporating in the"diazosystem a'latentjdei- -velo'per"whi'ch is activatibl'e by heat alonetobrihgabout the color forming reaction of this type jot system.v Theinvention -in this sense does not contemplate any fiinda} mental changein 'the chemical reactions that normally 'take 'pl'a'c'e, but rathermakes use of a class of composi} tions by which a-developerfo'r thediazo system is made physically present, but in a lateut, stable andunreactive manner. Latentdevelopers'cmployedinfthe compositions ofinvention constitute ing'ene'ral a class ofcoinpoiindswhich exist asstable, solid materials at normal conditioiis of temperature andhumidity and dissociate "at an elevated temperature to yield a base.Compounds of this known to the art constitute abase and; sane-r e poundwith which the base will crystallize and fauna stable crystal complexcontaining the base within a crystal lattice in the form of a distinct'plfysical chen iical entity. The latentdevejlop'ers,although'coiita'ining ab'asic component, do not exhibit substantialbasic prepares and may accordingly be incorporated in the 'di'azo systemwithout causing a dye forming reactionft o take place; They are,however, dissociable at relatively lc'u'ii' elevated temperatures andthe base is released in fully active condition and ma'deavailable forthe reaction. I

Latent developers most suitable for this inv n ibn" ai'e those stableunder conditions normally encountered in the manufacture, storage andshipment of'frnate'rials or this type. These conditions are referred toin this sped,- fica'tion and in the appended claims by the term normal?and may be typified by conditions of temperature below about 100 F. anda relative humidity less than 96 percent. The term is not used, hov'vefve'r, in an ass-ante sense, but rather with reference to thegeneral ian'ge of conditions one might expect to prevail undr actualconditions of use, and to the fact that dissociation -Will occur at somehigher temperature which is practically developers include in generalthe class of compounds" formed when a base, generally an amine, and a material which will crystallize with the base are "combined to form asolid stable material, which may desig netted a crystal complex,characterized bystab1 1ty at normal conditions of temperature andhumidity, ness with reference to its basic characteristics; and disc" 3sociability at a convenient elevated temperature to yield the base.

These latent developers include such crystal complexes as the co-crystaladducts of a bisphenol, and the in clusion compounds. Although thesevarious types of complexes are sometimes referred to as differentclasses of materials, they are for the purposes of the present inventionessentially the same with regard to the physical characteristicsrequired of a latent developer. In each case a base and carriercompound, i.e. a bisphenol or urea, are combined in a manner such thatthe resultant complex conceals the characteristics of the base andexists in stable, inert form, while dissociating at an elevated, butrelatively low, temperature to provide basic conditions. They aredesignated as complexes because the base and carrier compound arecombined or associated by a low energy bond.

Although certain specific compositions are herein designated as examplesof latent developers, it should be noted that one skilled in the art andfamiliar with this disclosure will not in any way be limited in aselection of suitable latent developers to the materials specificallyset forth. He may rather employ any composition comprising a basiccomponent combined with a carrier compound component to form a crystalcomplex, and having the requisite properties of inertness, stability anddissociability. The selection of such compositions may readily be madeon the basis of known, or readily determined, properties, as in any caseof selecting a material that possesses the characteristics required forits intended use. The chemical nature of the latent developer issignificant primarily in-that it must include a base effective toeffectuate a dye forming reaction in the diazo system, but such basesare well known to those skilled in this field of chemistry, and thisinvention is not otherwise concerned with the chemical aspects of diazosystems. When the base is released by the dissociation of the latentdeveloper the reaction that occurs is not essentially different fromthat occurring in the development of diazo systems by already knowntechniques. In this respect the invention relates to a physicalcombination of ingredients long known to be reactive, and is essentiallycharacterized by the way that the ingredients are combined in anunreactive manner.

The selection of a suitable latent developer can readily be made toprovide for a variety of characteristics in the copy sheet. Assumingthat a given base or class of bases, such as primary hydroxyl amines, isselected as the desired basic component on the basis of the knownchemistry of the reaction, and that numerous solid association products,or crystal complexes, of such an amine or amines with a bisphenol orurea will be available, the one having the desired characteristics ofstability, inertness, and activation temperature may then readily beselected on the basis of those characteristics which are known or easilydetermined with the aid of simple experiments within the skill of anyoneversed in laboratory technology. If for instance an activationtemperature of between 90 and 100 C. is desired, the various complexesmay be heated to within this range in the presence of a color indicatorto determine whether a basic condition is brought about. Anothersuitable procedure is to apply a sample of the various complexes to asheet of commercial ammonia developing type diazo paper, and then heatthe sheet to the desired range to see whether development occurs.

If stability is a factor, the various crystal complexes may be appliedto a diazotype sheet which may then be stored under test conditions,such as relatively high temperature and humidity, to determine whetherany development occurs.

These test procedures, it will be noted, involve purely manipulativesteps which determine the presence of properties on the basis of which aselection may readily be made without in the least involving anyinventive effort.

The latent developer may be incorporated in the diazotype sheet in anyof numerous ways, the only requirement being that it be presentthroughout the diazo system in potentially reactive association withthat composition. Heating of the sheet to cause dissociation of thecrystal complex and a release of the basic component will thus causeuniform development over the heated area. The latent developer may becombined with ordinary commercial diazotype copy sheets which containboth the diazo compound and the azo coupler, as a coating over thesensitive coating. In one preferred embodiment, the latent developer isdispersed in a solution of a binder and coated onto the sensitizedsurface of the diazotype sheet by conventional means. In some cases asolution of the latent developer may be formed and applied to thediazotype sheet. An alternative procedure is to form a coatingcomposition containing the diazo compound, azo coupler, and latentdeveloper in suspension, and applying this composition to paper or othersuitable backing material as a single coat.

Crystal complexes suitable as latent developers and currently known tothe art include in general organic bases co-crystallized with bisphenolcarrier compounds to form co-crystai adducts of the general typedescribed in US. Patent 2,829,175; and inclusion compounds of organicbases with urea as described in US. Patents 2,569,984 and 2,520,716.

Any amine otherwise suit-able as a basic developer for a diazotype sheetmay be employed including primary, secondary and tertiary aliphaticamines, alicyclic amines, aromatic amines, heterocyclic amines, hydroxylamines, but preferably an amine having highly basic characteristics ispreferred, e.g. hydroxyl amines, polyfunctional amines and primaryaliphatic and alicyclic amines.

Latent developers of the co-crystal adduct and inclusion compound typeare formed by dissolving the amine and the carrier compound in asutiable solvent and crystallizing out the co-crystal complex, which maythen be recovered and incorporated into a sutiable coating medium foruse as described herein.

Representative examples of this invention setting forth the best modepresently contemplated of carrying out the invention and representativetypes of latent developers which may be used are given below. In eachexample it will be seen that a latent developer is prepared ancl is thenincorporated in a diazotype copy sheet. The components of the diazotypesheet are themselves well known in the art and are not considered asconstituting per se any part of this invention. Such systems aredescribed in US. Patents 1,444,469 and 1,628,- 279.

In each of the following Examples 128 the carrier compound was firstdissolved in the solvent at a temperature of about F., and the base wasthen added and agitated for 30 minutes with a motor-driven stirrer. Themixture was then chilled for about 14 hours (overnight is sufiicient) atabout 30 F., during which a precipitate formed. The precipitate wasfiltered, washed thoroughly three times with n-hexane at roomtemperature (70 F.), filtered, and dried. In each case the resultingproduct constituted a latent developer. The examples set forth theproportions and identities of the several ingredients. All ingredientswere technical grade unless otherwise noted, and all operations werecarried out in glass vessels.

EXAMPLE 1 G. Carrier: Bisphenol A 113 Base: Isopropylamine 30 Solvent:Toluol 550 Product: Co-crystal adduct of isopropylamine and bisphenol A,M.P. 154-157" C.

EXAMPLE 2 v G. Carrier: Bisphenol A... 113 Base: Ethylene diamine 3OSolvent: Toluol A 1. 550 Product: Co-crystal edduct of bisphenol A andethylene diamine, M.P. 91-96" C.

EXAMPLE 3 Carrier; Blsfihenol A 113 Base: Cyclohexylamine 5-1 Solvent:Toluol 550 Product: (Jo-crystal adduct of bisphenol A andcyclohexylamine, M.P. 108-1l0 C.

EXAMPLE 4 Carrier: Eisphenol A 1 13 Base: Diethylamine Solvent: Toluol550 Product: Co-cr'ysta'l adduct of bisphenol A and cli- 'ethylamine,M.P. 117-153 C.

EXAMPLE 5 Carrier: Bisphenol A 113 Base: Di-n-pr.o1:yla1nine S1"Solvent: Toluol 55,0 Product: Co-crystal adduct of bisphenol A and "di-'n-propylamine, M.P. 154-156" vC.

EXAMPLE 6 Carrier: Bisphenol A 113 Base: Tributylamine L. '93 ;Solvent:Toluol "550 Product: (Io-crystal adduct of bisphenol A andt-ributylamine, M.P. 117-155 C.

EXAMPLE 7 Carrier: Tetrachlorobisphenol A 183 Base: Diethanolamine 5 3Solvent: Toluol 364 Product: Co-crystal adduct of tetrachlorobisphenol Aand diethanolamine, M.P. '144-149 C.

EXAMPLE -8 "Carrier: Tetrachlorobisphenol A 182 Base: Diethy'lamine 37Solvent: Toluol 364 Product: Co-crystal adduct of tetrachlorobispl'renolA and 'diethylanrine, M.P. -142--175 C.

EXAMPLE '9 Carrier: Tetrachlorobisphenol A 182 Base:H-ydroxyethyldiethylenetriamine 75 .Solvent: To'luol 364 Product:Co-crystal adduct of tetrachlorobisphenol A andhydroxyethyldiethylenetriamine, M.P. 93-

EXAMPLE '10 Carrier: Tetrachlorobisphenol A; 182 Base: Isooctylamine -65.Solvent: Toluol 364 Product: Co-crystal adduct of isooctylarnine andtetrachlorobisphenol A, M.P. 172-185 C.

EXAMPLE 1 1 G. "Carrier: Tetrachlorobisphenol A 182 Base: N-decylamine75 Solvent: Toluol 364 Product: Co-crystal adduct of n-decylamine andtetrachlOrobisphenol A, M.P. l92-198 C.

6 EXAMPLE 12 a G. Carrier: Tetrachlorohiephenol A 182 Base:Tributylamine 93 Solvent: Toluol v 364 Product: Co-crystal adduct oftributylamine and and tetrachlorobisphenol A, M.P. -1 12 C.

EXAMPLE 13 Carrier: Tetrachlorobisphenol A 182 Base: Triethanolamine v75 Solvent: Toluol 364 Product: Co-crystal adduct of triethanolarnineand tetrachlorobisphenol A, M.P. 134l40 C.

EXAMPLE 14 Carrier: 'Tetrachloroblsphenol A 182 Base: Ethanolamine 31Solvent: Tolunl 364 Product: Co-crystal adduct of ethanolamine andtetrachlorobisphenol A, M.P. 96-104 C.

EXAMPLE 15 Carrier 4,4-thio-bis-(6-tert. b1ity1-m-cresol) 144 Base:Ethylene diarnine 310 Solvent: Stoddard solvent 200 Solvent: Toluol 800Product: Co-crystal adduct of ethylene diamine and 4,4-thio-bis (6-tert.butyl m-cresol), M.P. 112- 115 C.

EXAMPLE 16 Carrier: 4,4'-thio-bis-(-6-tert. butyl-n1-creso1 144 Base:Cyclohexylamine 51 Solvent: Stoddard solvent 200 Solvent: Toluol- I V V800 Product: Co-crystal adduct of cyclohexylamine and 4,4"-thio-'bis-'(6-tert. butyl-m c're'sol), M.P. 79- 96'C.

EXAMPLE '17 Carrier: 4,4 butylidene bis (6 tert. butyl m eresol) 161Base: Ethylene diamine 37 Solvent: Stoddard solvent 200 Solvent: T0lu01800 Product: Co-crystal adduct of ethylene diamine and4,4'-butylidene-bis-Q6 tert. butyl-m-cresol), 212 246 C.

EXAMPLE 18 Carrier: 4,4-butylidene-bls-(6-tert. butyl-m-cre 01,) iBase:.N- methy-lethanolamine."A 38 Solvent: Stoddard solvent; H A v Solvent:T011101. E 800 Product: Co-crystal adduct of N-met ylethanol amine and4,4 -butylidene bis-,(6-tert. .butyl-mcreso1),'M.P. 2-13-216 .C.

' EXAMPLE 19 carrier; 4,4 -'butylidene-bis-(6-tert. butyl-m-cresol) e 6Base Tetrarnethylg'uanidine A 5 8 Solvent: Stoddard solvent 200 Solvent:Toluol .800

Product: (Do-crystal adduct of ,te'tramethylguanidine and4,4'-blutylidene-bis-(6-tert. butyl-m-creso l), M.P. .183--C.

EXAMPLE 20 "Carrier: 2,2T-methylene-bis-j(44methyl 6-tert. butyl p 141)Base: Diethanolamine 53 'Solvent: Stoddard s0lvent 560 2,2 methylene -'bis-(4-rnethy1-6-tert. butyl .phe- 'nol), M.P. 110-117" C.

7 EXAMPLE 21 G. Carrier: Tetrachlorobisphenol A 182 Base:Z-amino-l-butanol 44.5 Solvent: T011101 364 Product: Co-crystal adductof 2-amino-1-butanol and tetrachlorobisphenol A.

EXAMPLE 22 Carrier: Tetrachlorobisphenol A 182 Base:Monoisopropanolamine 37.5 Solvent: Toluol 364 Product: Co-crystal adductof monoisopropanolamine and tetrachlorobisphenol A.

EXAMPLE 23 Carrier: Tetrachlorobisphenol A 182 Base:Methyldiethanolamine 59.5 Solvent: Toluol 364 Product: Co-crystal adductof methyldiethanolamine and tetrachlorobisnhenol A.

EXAMPLE 24 Carrier: Tetrachlorobisphenol A 182 Base: Propylenediamine(70%) 53 Solvent: Tolnol 364 Product: Co-crystal adduct ofpropylenediamine and tetrachlorobisphenol A.

EXAMPLE 25 Carrier: Tetrachlorobisphenol A 182 Base:2-amino-2-ethyl-l,3-propanediol 59 Solvent: Toluol 364 Product:Co-crystal adduct of 2-amino-2-ethyl-1,3-

propanediol and tetrachlorobisphenol A.

EXAMPLE 26 Carrier: Bisphenol A 113 Base: Isobutylamine 36 Solvent:Tolunl 550 Product: Co-crystal adduct of isobutylamine and bisphenol A.

EXAMPLE 27 Carrier: Bisphenol A 113 Base: Dimethylaminopropylamine 51Solvent: Toluol 550 Product: Co-crystal adduct ofdimethylaminopropylamine and bisphenol A.

EXAMPLE 28 Carrier: Tetrachlorobisphenol A 182 Base: Aminobispropylamine66 Solvent: Toluol 364 Product: C-crystal adduct of aminobispropylamineand tetrachlorobisphenol A.

In the foregoing examples the bisphenol A and the tetrachlorobisphenol Awere commercial products. The 2,2-methylene-bis-(4-methyl-6-tert. butylphenol) is sold as Antioxidene 2246. The 4,4'-thio-bis-(6-tert.butyl-mcresol) is sold as Santowhite crystals, and4,4-butylidenebis-(6-tert. butyl-m-cresol) is sold as Santowhite powder.

The co-crystal adduct formed in each of the preceding Examples 1-28 wasincorporated into a standard ammonia developing diazotype paper, e.g.Ozalid paper, by the following technique: Ten grams of the co-crystaladduct were dispersed in 50 g. of a 1.5 percent solution ofpolyvinylethylether dissolved in hexane, by milling the co-crystaladduct with the solution for four hours in a ball mill operating in achilled room at 40 F. The dispersion was coated by means of a Mayer rodonto the diazotype paper to a dry weight of 3-5 pounds/ 3000 squarefeet, and the paper was then dried. Samples of the dry treated sheetwere exposed to a master under ultraviolet light in accordance withstandard practice, and the sheet was then heated for five seconds on ahot plate heated to 300 F. In each case a clear and legible copy of themaster was formed.

In each of the foregoing examples the polyvinylethylether solutionserves as a mechanical binder by which the latent developer is retainedin potentially reactive association with the underlying diazocomposition. Other film forming materials such as methylmethacrylatepolymer, vinyl chloride polymers, polyvinylalcohol, natural resins andgums and similar materials may also be used when dissolved in suitablesolvents which are not solvents for the crystal complex. Where thesolvent will also dissolve the crystal complex, the base may becomereleased in reactive form and cause premature dye formation within thediazotype system. It has been found, however, that certain crystalcomplexes do not result in base release when dissolved. For instance,the co-crystal adduct of diethanolamine and2,2'-methylene-bis-(4-methyl-6-tert. butyl phenol) described in Example20 may be dissolved in trichloroethylene or in octane and coated upon astandard ammonia developing diazotype paper without prematuredevelopment.

In the following examples the use of crystal complexes other than theadducts of an amine and a bisphenol are described. In Examples 29-31,the carrier compound was first dissolved in the solvent at a temperatureof about 150 F. and the solution was then left to stand overnight (14hours) at room temperature (70 F.). The base was then added withmechanical stirring, and the solution was then again left to standovernght (14 hours) at room temperature (70 F.) during which aprecipitate formed. The precipitate was filtered out, washed thoroughlythree times with n-hexane at room temperature (70 F filtered and dried.In each case the resulting product constituted a latent developer. Theexamples set forth the proportions and identities of the severalingredients, all of which were technical grade unless otherwiseindicated. All mixing operations were carried out in glass vessels.

EXAMPLE 29 Carrier: Urea Base: Di-n-hexylamine 45 Solvent: Methanol 396Product: Inclusion compound of di-n-hexylamine in urea.

EXAMPLE 30 Carrier: Urea 90 Base: Di-n-butylamine 45 Solvent: Methanol396 Product: Inclusion compound of di-n-butylamine in urea.

EXAMPLE 31 Carrier: Urea 98.8 Base: N-decylamine 49.4 Solvent: Methanol434.2

Product: Inclusion compound of n-decylamine in urea.

The inclusion compounds formed in each of the preceding Examples 29-31was incorporated into a standard ammonia developing diazotype paper,e.g. Ozalid paper, by the following technique:

Nine and one-half grams of the inclusion compound were dispersed in g.of a 5 percent solution of methylmethacrylate polymer (Acryloid 8-82)dissolved in toluol, by milling the inclusion compound with the solutionfor 4 hours in a ball mill operating in a chilled room at 40 F. Thedispersion was coated by means of a Mayer rod onto an ammonia developingdiazotype sheet to a dry weight of about 3 pounds/3000 square feet, anddried. The dry sheet was exposed through a master to ultraviolet lightaccording to standard practice, and was then heated for 5 seconds on ahot plate heated to 350 F. In each case a clear and legible copy of themaster was formed.

In the following examples the latent developer is combined with thecomponents of the diazotype system, and

ammo? 9 then coated upon a suitable support. A single coating is thusformed which is itself light-sensitive and heat-developable.

EXAMPLE 32 The following ingredients in the following amounts werecharged into a ball mill:

P-olyvinylthylether, 25% solution in heptane 480 The'components weremilled 'to'getherfor 4 hours in a roomchilled to 40 F. Twenty-five gramsof the diazo system composition p'repared'in the ball mill and 'g. ofthe co=crystal addu ct prepared in Example 11 and 25 g. of hexane werecombined in a ball mill and milled for 4*hours 'in a room chilled to 40F. to disperse the cocrystal adduct in the diazo system composition. Themixture was then coated by a Mayer "rod to a-dry weight of approximately3 pounds/ 3000 square feet'on a 60 pound chromekote paper, and dried.The dried sheet was ex- "posed to ultraviolet lightthrough a master andthen heated for 5 seconds at 350 F. to produce a legible copy of the-master.

EXAMPLE 33 Twenty-five grams of the diazo system composition ,preparedin Example 32, 5 got the co-crystal adduct prepared in Example 10, and25 g. of a 2 percent solution .of .Acryloid B32 dissolved intrichloroethylene were anixedtogether in aball mill for 4 hours inaroomchilled -to40 F. The mixture wasapplied by means'ofa Mayer .rod to adry weight of approximately 3 pounds/3000 square feet to a 60 poundchromekote paper, and dried. The dried. sheet was :exposed toultraviolet light through a master and then heated at 350 F. for 5seconds toprowide a legible copy of the master.

In selecting "a particular latent developer, the lowest temperature atwhich development will occur within a -reasonablevheating time will "beof dbviousinte'rest. This may be considered as the temperature at Whichdissociation of the latent developer occurs with the release of its'basic component. That temperature is referred to herein -'as the baserelease temperature. Anexper'imental prorcedure to determine the baserelease temperature of a latent developer -'is "as follows:

BaseRelease Test 1A'coating dispersion is formed 'by charging a ball'mill with '100 grams df latent developer, and 500 grains of a 2 /2percent solution of polyvinylethylether (Bakelite FEDBM) in hexane, andmilling for 15 hours. The comiposition is then coated onto gl-as's'ineto-give a coating hav- -irig a dry weight of 2-3 pounds/3000 squarefeet, and dried. The coated glassine is then cut into a striptinequarter inch wide, andiplaced coated side down against ran indicatorpaper (e. g. pH ydrion, -"6&08;0 pH range, in which the essentialingredient is a Sulfonphthaleininditcator) on a *hot plate. A corkstopper hau ing its me :cut"-toione-quart'er inch in Width is placedcrosswise over the "coated rglas'sine strip to i give a contact area ofone- -qnarterinch by one-quarter inch and is weighted with a 500 gramWeight. The temperature of 'the plate is raised by increments of 5 F.,each step being maintained for t1 minute, and the lowest temperature atwhich a col-or fehang'etakes place is'noted. I

The same "procedure may he employed using a 'commercial ammoniadeveloping 'dia'z'otype paper, preferably one designated as slow speed(which has a low acid content) such as Tecnifax 25-8. When the latentdeveloper "does :not contain an ionizing medium, the use of standardindicator papers cannot be relied upon since the the color change maynot occur in the absence of such medium. The use of a standard ammoniadeveloping -diazotype sheet is therefore better suited for determiningthe base release temperature of "such "latent develo'pers. I

The base release temperature, determined as outlined above, for severalof the latent developers described in the examples are given in Table I.

TABLE -1 Base release temperature, 'F., as determined with- Example ITecnifa'x A pHydrion a (60-810 25-8 Generally, suitable latentdevelopers will have a base release temperature, determined 'asdescribedabove, above about 110 F. and preferably above about 140 F. The time andtemperature of development are frequentlyinterrelated in thatdevelopment may occur within shorter periods at higher temperatureswhile requiring longer periods at lower temperatures. The base releasetemperature will necessarily reflect this interrelationship and itsvalue in a given case :will depend on the conditions under which:it5ismeasured. The !procedure set forth is useful for purposes of comparisonas a standardized 'reference, and-in view-of the long durationat whichthe'sarnpies are maintained at each temperature step, the results willapproximate the absolute minimum at which release of the base from thelatent developer will-occur. It is conceivable, however, that release ofthe base will occur atlower temperatures within longer periods of time,or that the temperature may momentarily be raised to above the rep ortedbase release temperature for "shorter periods of time.

In addition to the base release temperature, a factor "relating to theselection of particiilar latent developments is the stabilityofthedeveloper and its reactivity or inertness toward the particulardiazo system. This may be most readily determined by coating adispersion of the developer onto an ammonia developing diazo sheet, andthen subjecting the sheet to actual, or simulated exaggerated,conditions of storage. A latent developer having the desiredcharacteristics inaythen be selected and a comparison of variousdevelopers may be readily made.

The reaction of the base in causing development or diazo systems is notfully understood, but it is known that a stable composition requiresthat the diazonium compound be in the form of itsacid salt andadditional acidic compounds are frequently included in diazo systems toimprove their stability. The base apparently serves to neutralize theacids present in thesystem and also to convert the diazonium salt to itsmore reactive base form. Since the acidity or acid content of differentdiazo systems will' be different, different amounts of base are requiredfor development, but in any'event the amount required for any givensystem may easily be determined experimentally if it is not alreadyknown.

The amount of latent developer required in any given application willdepend on the amount of base required for development, which will inturn depend upon the nature, including the acidity, of the diazo system.No precise amount can be set forth as a proportion of the compositionexcept according to the general rule that sufficient base must bepresent to effect development, and the determination of that amount iswell Within the abilities of one skilled in the chemistry of diazotypeprocesses.

The nature of the image formed in any particular system will bedetermined by the precise nature of the diazo components, and it shouldhere be noted that any of the diazo systems known to the art will besuitable. The compositions of Examples 32 and 33 employ conventionaldiazo compounds and azo couplers, but others may also be employed withcomparable results. For example, the following diazo compounds may beused:

ZnCI -P-diazo-N-dimethylphenylenediamine ZnCl -diazo compound of4-(N-methyl-N-hydroxyethylamino) -aniline2,l-diazohydroxynaphthalene-S-sulfonic acid ZnCl -diazo compound ofN-ethanol-ethylarninol-aminobenzene Zncl -P-diazodimethylaniline ZnCl-tetrazodiphenylpiperazine ZnCl -N,N-diethylaniline-P-diazoniumchlorideZnCl -N,N-dimethylaniline-P-diazoniumchloride ZnCl-4-N,N-diethylaminobenzenediazoniumchloride ZnCl-4-N,N-benzyl-N-ethylbenzenediazoniumchloride ZnCl-P-diazo-N-rnethyl-N-hydroxyethylaniline ZnCl-P-diazo-N-ethylarnino-o-toluidine CdCl-N-ethylaniline-P-diazoniumchloride CdCl-N-methylaniline-P-diazoniumchloride ZnCl-N-hydroxyethylaniline-P-diazoniumchloride ZnCl-N-propylaniline-P-diazoniumchloride 2,5,4-triethoxydiphenyl-1-diazoniumacid sulfate Naphthalene-Z-diazo-l-oxide-S-sulfonic acidP-diethylaminobenzenediazoniumborofiuoride ZnCl-4-benzoylamin0-2,S-diethoxybenzenediazoniumchloride P-phenylaminebenzenediazonium sulfate ZnCl-N-hydroxyethyl-N-methylamino-P-benzenediazoniumchloride ZnCl-1-(N-hydroxyethyl-N-ethyl) amino-3-methyl-4- benzenediazoniumchloride2,5,4'-triethoxydipheuyl-4-diazouiumacid sulfate ZnCl-l-benzoylamino-2,5-diethoxy-4-benzenediazoniumchloride ZuCI-l-ethylamino-3-methyl-4-benzenediazoniumchlo.

ride ZnCl -4-( N-methyl-N-hydroxymethyl) aminobenzenediazoniumchlorideThe diazonium components of the compounds above which are metaldichloride complexes may also be used.

Azo couplers which may be used include:

2,3-dihydroxynaphthalene-6-sulfonic acid resorcinolN-fi-hydroxyethyl-a-resorcylamide a-ResorcylamideN-phenyl-a-resorcylamide Mono-a-resorcylamide of ethylene diaminePhloroglucinol dihydrovynaphthalene Na-naphthalene 1,3,6-trisulfonicacid Phenylmethylpyrazolone diresorcinolsulfoxide7-hydroxy-l,Z-naphthimidazole resorcinolmonoacetateresorcinolmonocarbazate resorcinol-mono-N- (B-aminoethyl) carbamateresorcinol-mono-N,N-diethylcarbamate resorcinol-mono-ethylcarbonateZ-diethylaminoethylresorcinolmonobenzenesulfonateZ-hydroxyphenylthiourea Z-hydroxyphenylthiourea 4-hydroxyphenylthiourea6-methyl-4-hydroxy-2 1)-pyridone6-ethyl-4-hydroxy-l-methyl-2(1)-pyridone Typical diazo systems willgenerally include, in addition to a diazonium compound and an azocoupler, other materials such as stabilizing acids and otherstabilizers. Typical stabilizing acids are: citric acid, maleic acid,formic acid, phosphoric acid, tartaric acid, boric acid, hydrochloricacid, ascorbic acid and isoascorbic acid; and other stabilizers include:thiourea, zinc chloride, aluminum sulfate. Other types of diazo systemsutilize a single diazonium compound, which upon exposure to actinicradiation decomposes to form an azo coupler compound. A brief exposureof such a compound will result in partial decomposition and form acoating containing undecomposed diazonium compound and the decompositionproduct, an azo coupler. Such are described in US. Patent No. 2,313,288.

As shown in the examples described above, photocopy sheets provided bythis invention may be exposed to the master in the same way asconventional diazotype paper, but development of the latent image ismuch more easily accomplished simply by heating the paper. Anotherconvenient method of making use of the photocopy paper of this inventionis to use a light source rich in both ultraviolet and infrared radiationby which the paper may be simultaneously exposed and developed. Standardduplieating equipment of the type used for exposing thermofacsimile mayalso be used. It should be noted in this connection that thethermofacsimile process is also suitable since infrared radiation of thedark areas will cause selective heating and develepoment of thediazotypc paper there, without affecting the light areas. Subsequentexposure of the sheet to ultraviolet light will then destroy thediazonium compound in the light areas and obviate the possibility offurther darkening therein.

In this connection it will be noted that the systems of this inventionmay employ, in place of the diazo components, the color indicatormaterial utilized in the procedures reported in Table 1 which alsochanges color in the presence of a basic organic amine.

The foregoing description sets forth in detail the technical aspects ofthis invention and describes representative examples of compositions andprocedures that may be employed in its practice. These are given tofamiliarize those skilled in the art with its advantages and featuresand to set forth not only various specific compositions that may beused, but also procedures by which suitable materials other than thoseherein described may be selected and the full scope of applicantscontribution may be made use of.

A commercially useful heat developable photosensitive composition haslong been sought but without practical success. Suggestions that havebeen advanced have included the incorporation of heat activatablematerial which is potentially reactive with the constituents of thediazo system, but none of the systems heretofore proposed has provided acommercial commodity. Potentially reactive developers suggested in thepast have for the most part been in the nature of solid materials whichthemselves are reactive, as when heated or dissolved, but which remainrelatively dormant in the system until heated, whereupon theirreactivity is increased. As an example, urea and dimethylurea may beincluded in the diazonium composition, as shown by Morrison in US.Patent No. 2,732,- 299, to provide a relatively stable composition whichis described as requiring a rather long development (1 minute) at a highdeveloping temperature of C.

Both urea and dimethylurea have been tried as latent developers inconnection with the present development, but they have been found toproduce a result quite difapropos ferentfrom that attained byraean's i'the latent developers employed in compositions of this invention. Bothof these compounds caused an irregular, gradual darkening when the paperwas heated; -first the area just outside the heated portion turned blue(when employing a bluedeveloping diazotype sheet) and then the heatedarea reddened. Apparently, as the urea was heated to activationtemperature, there was initially a decomposition which formed ammoniavapors causing development just outside the heated area. Continuedheating caused melting of the urea, and some kind of color-formingreaction resulted. This type of reaction, marked by bringing the urea,or dimethylurea, to reactive conditions, was in marked contrast to themechanism of applicants system wherein the dissociation of the crystalcomplex releases the base in a fully reactive state. The practicalsignificance of this is instantaneous and complete color formation uponreaching the developing temperature.

By way of example, it will be noted from Table I that the latentdevelopers of Examples 30 and 31 both employ urea, not as a developerbut as the carrier compound. These show base release temperatures of 225F. and 115 F. respectively. The same test, using urea alone as though itwere a latent developer, coated from its aqueous solution onto glassinepaper, shows with Tecnifax 25-S paper a blue color formation in the areasurrounding the test area at 170280 F., and a reddening in the contactarea at 245280 F. With dimethylurea, the initial blue color formationoutside the contact area occurred at 260- 290 F. with reddening in thecontact area at 260290 F.

Ammonium carbonate may also be employed as a kind of potential developeras shown by Dieterle in US. Patent No. 2,228,562. It is activatable at amuch lower temperature than urea and its derivatives but may not bepreliminarily combined with the diazonium system since development willoccur even at room temperature after a relatively short period of time.This material is neither inert nor stable. Neither of these systemswhich have heretofore been suggested has made use of a latent developerwhich is both stable and inert at normal conditions of temperature andhumidity while being dissociable at an elevated temperature to yield abase in fully reactive state effective to cause instantaneous andcomplete development.

Photothermographic papers embodying this invention stand in markedcontrast to the diazo systems proposed in the past. They possess thegeneral advantageous characteristics of conventional diazotype papers,but are easily developed completely by heating to temperatures rangingupwards from the base release temperatures reported by an amountdepending on the time of heating. Development occurs by release of thebase from the latent developer in already reactive condition, and thereaction occurs quickly and completely upon heating within periods oftime as short as a few seconds. Processing of the paper other than byheating is entirely unnecessary; the image originally formed is stableand since exposureto ultraviolet light has destroyed the diazoniumcompound in the exposed, undarkened areas, there is no danger ofsubsequent development in these areas.

We claim and desire to secure by Letters Patent:

1. A heat developable photo copy composition comprising a potentiallyreactive photosensitive azo dyeforming material in stable unreactivecondition but reactive with a basic organic amine to form a dye and astable, unreactive latent developer in potentially reactive associationwith said material, said latent developer being an organic amine incombination with a bisphenol forming a solid crystalline complex whichis stable undernormal conditions of temperature and humidity anddissociable at said activation temperature to yield said amine.

2. A heat developable photo copy composition comprising a potentiallyreactive photosensitive azo dye-forming material in stable, unreactivecondition but reactive with a basic organic amine to form a dye and astable untemperature to yield said amine.

1-4 reactive 'lafent developer in potentially reactive association withsaid material, said latent developer being an organic amine incombination with urea forming a solid "inclusion compound which isstable under normal conditions of temperature and humidity anddissociable at said'activation 3. A photosensitive heat developable copysheet com prising a support carrying a potentially reactivephotosensitive azo dye-forming material in stable, unreactive conditionbut reactive with a basic organic amine to form a dye, and a latentdeveloper in potentially reactive association with said material, saidlatent developer being an organic amine in combination with a bisphenolforming a solid crystalline complex which is stable under normalconditions of temperature and humidity and dissociable at saidactivation temperature to yield said amine.

4. A photosensitive heat developable copy sheet comprising a supportcarrying a potentially reactive photosentitive azo dye-forming materialin stable, unreactive condition but reactive with a basic organic amineto form a dye, and a latent developer in potentially reactiveassociation with said material, said latent developer being an organicamine in combination with urea forming a solid inclusion compound whichis stable under normal conditions of temperature and humidity anddissociable at said activation temperature to yield said amine.

5. A photosensitive heat developable copy sheet comprising a supportcarrying a potentially reactive photosensitive azo dye-forming materialin stable, unreactive condition but reactive with a basic organic amineto form a dye, and a coating containing a latent developer uniformlydistributed over said material and in potentially reactive associationtherewith, said latent developer being an organic amine in combinationwith a bisphenol forming a solid crystalline complex which is stableunder normal conditions of temperature and humidity and dissociable atsaid activation temperature to yield said amine.

6. A photosensitive heat developable copy sheet comprising a supportcarrying a potentially reactive photosensitive azo dye-forming materialin stable, unreactive condition but reactive with a basic organic amineto form a dye, and a coating containing a latent developer uniformlydistributed over said material and in potentially reactive associationtherewith, said patent developer being an organic amine in combinationwith urea forming a solid inclusion compound which is stable undernormal conditions of temperature and humidity and dissociable at saidactivation temperature to yield said amine.

7. A heat marking copy sheet responsive to heating to an elevatedactivation temperature by changing visibly to a contrasting colorcomprising, in combination, a support carrying indicator material whichchanges color in the presence of a basic organic amine, and a stableunreactive latent heat sensitive developer in intimate association withsaid material for causing a color change upon heating said sheet to anactivation temperature greater than F., said developer being an organicamine in combination with a bisphenol forming a solid crystallinecomplex which is stable under normal conditions of temperature andhumidity and dissociable at said activation temperature to yield saidamine to cause said color change.

8. A heat marking copy sheet responsive to heating to an elevatedactivation temperature by changing visibly to a contrasting colorcomprising, in combination, a support carrying indicator material whichchanges color in the presence of a basic organic amine, and a stableunreactive latent heat sensitive developer in intimate association withsaid material for causing a color change upon heating said sheet to anactivation temperature greater than 110 F., said developer being anorganic amine in combination with urea forming a solid inclusioncompound which is stable under normal conditions of temperature andhumidity and dissociable at said activation temperature to yield saidamine to cause said color change.

(References on following page) References Citeai in the file of thispatent UNITED STATES PATENTS Dieterle Jan. 14, 1941 Barde Mar. 9, 1943Greig Sept. 22, 1953 Morrison I an. 24, 1956 16 Van Dam July 28, 1959OTHER REFERENCES Saunders: The Aromatic Diazo Compounds, Edward 366 and368.

5 Arnold & Co., London, 1949, page 365, lines 19-23, pages

3. A PHOTOSENSITIVE HEAT DEVELOPABLE COPY SHEET COMPRISING A SUPPORTCARRYING A POTENTIALLY REACTIVE PHOTOSENSITIVE AZO DYE-FORMING MATERIALIN STABLE, UNREACTIVE CONDITION BUT REACTIVE WITH A BASIC ORGANIC AMINETO FORM A DYE, AND A LATENT DEVELOPER IN POTENTIALLY REACTIVEASSOCIATION WITH SAID MATERIAL, SAID LATENT DEVELOPER BEING AN ORGANICAMINE IN COMBINATON WITH A BISPHENOL FORMING A SOLID CRYSTALINE COMPLEXWHICH IS STABLE UNDER NORMAL CONDITIONS OF TEMPERATURE AND HUMIDITY ANDDISSOCIABLE AT SAID ACTIVATION TEMPERATURE TO YIELD SAID AMINE.
 4. APHOTOSENSITIVE HEAT DEVELOPABLE COPY SHEET COMPRISING A SUPPORT CARRYINGA POTENTIALLY REACTIVE PHOTOSENSITIVE AZO DYE-FORMING MATERIAL INSTABLE, UNREACTIVE CONDITION BUT REACTIVE WITH A BASIC ORGANIC AMINE TOFORM A DYE, AND A LATENT DEVELOPER IN POTENTIALLY REACTIVE ASSOCIATIONWITH SAID MATERIAL, SAID LATENT DEVELOPER BEING AN ORGANIC AMINE INCOMBINATION WITH UREA FORMING A SOLID INCLUSION COMPOUND WHICH IS STABLEUNDER NORMAL CONDITIONS OF TEMPERATURE AND HUMIDITY AND DISSOCIABLE ATSAID ACTIVATION TEMPERATURE TO YIELD SAID AMINE.